In a large bowl, combine the shredded chicken, mashed avocado, ranch dressing, garlic powder, onion powder, salt, and pepper. Mix until well combined.
Lay out the flour tortillas on a clean surface.
Evenly distribute the chicken mixture onto the center of each tortilla, leaving about 1 inch of space around the edges.
Top the chicken mixture with shredded cheddar cheese, chopped lettuce, and diced tomato.
Fold in the sides of each tortilla, then roll it up tightly from the bottom to the top.
Place the burritos seam-side down on a plate or in a baking dish.
If desired, you can lightly toast the burritos in a skillet over medium heat for 2-3 minutes on each side to crisp them up.
Serve immediately, or wrap in foil and refrigerate for up to 2 hours before serving.